But in Jakarta, the nation’s capital, groundwater extraction remains the main culprit behind land subsidence, as up to 65 percent of its residents rely on underground water sources. Land subsiding is anywhere from 3 to 18 cm annually in various parts of the city and a lack of mitigation would lead to 30 percent subsidence in 2050, Abdul Malik Sadat Idris, an official from the National Development Planning Agency, warned in February.

“Land subsidence is obvious along the northern coastline of Java at a rate of 1 to 25 cm annually,” said Dr Heri Andreas, a geodesist from Bandung Institute of Technology (ITB) in West Java. “This trend is a warning for us that land subsidence will continue to happen unless we do something to stop or withhold it, since land subsidence is like a silent killer that will affect our communities as it causes inundation and land to erode.”

Indonesia’s 54,700 kilometer coast line is the second-longest in the world after Canada, and its mangrove ecosystem is the largest in the world, covering 3,489,141 hectare or 23 percent of the world’s mangrove ecosystem, according to data from the Ministry of Environment and Forestry.

These mangrove forests are part of an estimated 30 million-hectare coastal area ecosystem along with peatlands, wetlands, lagoons, river deltas, sea bank, marshes and evaporation ponds, many of which are located close to human settlements that are less than 30 meters above sea level.

They support to a wealth of life as a natural habitat for various species, and also serve as a buffer to seawater intrusion. At the same time, they store fresh water and contain high carbon reserve that help mitigate climate change. A mangrove forest that extends at least 100 meter inland could suppress rising tide by 13 percent to 66 percent.

“But most of our wetlands and 52 percent of our mangrove forests have been destroyed. We have lost 85 percent of the mangrove areas on the northern coast of Java as they have been converted to human settlements or man-made fish ponds. In some areas, the sea level has even risen,” said Agung Kuswandono, a deputy minister in charge of natural resources coordination at the Coordinating Ministry of Maritime Affairs.

Nyoman Suryadiputra, director of Wetlands International Indonesia said the only course of action now is an immediate halt to wetlands conversion.

“Many of us don’t realize the fact that Indonesia’s largest fresh water reserves are in peatlands instead of lakes or rivers,” he said, adding that at the same time, climate change also causes sea level to rise and these two situations are increasing the risk of further calamities along the coastline.

Jakarta is not the only city in the region suffering from land subsidence. Other Asian mega cities such as Tianjin, Shanghai, Tokyo, Osaka, Manila, Bangkok, Dhaka, and Bombay also have some areas that have slipped below sea level, said Dr Athanasios Vafeidis from Department of Geography, Coastal Risks and Sea-Level Rise of Kiel University in Germany.

According to Vafeidis, calamity could be prevented if people are willing to adapt to the sea level rise and prepare for it by looking at data and historical facts. Planning based on such knowledge is less costly compared to the damage that could result from ignoring the facts, or having to take action after the fact.

“Adaptation costs are generally lower than direct damage costs. If we include indirect impacts, benefits are even larger,” Vafeidis told a group of visiting international journalists to the institution in late 2017 organized by

“The costs depend on the timing of adaptation but proactive adaptation pays,” he said.

Dr Vafeidis added that the rise in sea level has been accelerating for the past decade and will continue to do so. The rates the same but some regions could see acceleration three times faster than others. Without adaptation, he said, many areas will become unviable by 2100.

“A better understanding of adaptation and decision-making under certainty is essential, especially for vulnerable regions such as deltas and small islands,” he said.

Klaus Schwarzer from Institute of Geosciences, Sedimentology, Coastal and Continental Shelf Research at Kiel University, cited the Mekong in Vietnam, Chao Praya in Thailand and Mahakam in Indonesia’s Kalimantan island as examples of deltas that are vulnerable, based on current estimates of the relative sea level rise to 2050, including land subsidence in the deltas.

If no adaptions are in place, the number of people displaced from the Mekong delta would be extreme at more than one million, while anywhere from 5,000 to 50,000 people would have to flee their communities along the Chao Praya and Mahakam.

Schwarzer said more research on coastal zones would be essential to provide knowledge that could be applied in drafting potential future scenarios so that people can continue to make use of the coastal environment. However, such usage must be sustainable with better management of coastal ecosystem resources, given that some 2.8 billion people in the world now live within 100 km of a coast.

Mangrove forests that help to keep the tides at bay continue to be cut down, but very few people are talking about the loss of this essential element of coastal protection, said Martin Zimmer, a professor for mangrove ecology at Bremen’s University of Bremen.

Zimmer said researchers are developing an approach mangrove spatial conservation that focuses on humans needs while also maintaining biodiversity.

“It is an ecosystem design that focuses on what people in the area need. We implement an ecosystem that functions for them, not just to make the areas look beautiful. To protect coastal areas, we can’t just build dykes or other structures, but we do that with something that is naturally there, which is mangrove,” Zimmer said.

Coastal zones serve as an essential lifeline for much of the world’s population, Schwarzer said, given 95 percent of international trade involves marine transport, which ends up in harbors.

Oceans are also important sources of food with 90 percent of the world’s fishery activity is carried out in coastal zones.

“There is an increase in extreme storm surges and predictions of sea level rise. Coastal erosion already endangers about one-third of the world’s population,” Schwarzer said.